The present invention is directed in general to wireless telecommunication techniques. More particularly, the invention provides a method and system for sensing noncontiguous channels in a wireless network. Merely by way of example, the invention has been applied to a Wireless Regional Area Network (WRAN) system as defined in the IEEE 802.22 standard. But it would be recognized that the invention has a much broader range of applicability. For example, the invention can be applied to other wireless communication systems utilizing noncontiguous channels.
The IEEE 802.22 Wireless Regional Area Network (WRAN) system is designed to operate in the VHF/UHF TV broadcast bands between 54-862 MHz. According to IEEE 802.22, the system is formed by base stations (BS's) and customer premise equipments (CPE's). In the context of this application, a BS refers to a generalized equipment set providing connectivity, management, and control of the CPE, and a CPE refers to a generalized equipment set providing connectivity between subscriber and a BS. For example, a CPE may include an Access Point (AP). In a WRAN, the CPE's will be attached to a BS via a wireless link in the frequencies mentioned above. FIG. 1 shows a diagram illustrating a WRAN cell 100 including a BS 101 and a plurality of CPE's. e.g. 102 and 103, etc. The BS controls the medium access for all the CPE's attached to it.
Because there are incumbent systems operating in the TV broadcast frequency bands, the system needs have the cognitive capability of detecting the presence and possibly the locations of these incumbent systems and perform dynamic frequency selection so as to avoid creating interference. A WRAN Base Station is capable of performing a distributed sensing, and the CPE's sense the spectrum and send reports to the BS informing it about what spectrum availability. Two different types of spectrum measurement are generally performed by the CPE, i.e., in-band and out-of-band. The in-band measurement includes sensing the actual channel that is being used by the BS and CPE, whereas the out-of-band measurement includes sensing the rest of the channels.
Distributed sensing is used so that the measurements of a plurality of sensors, which are consumer premise equipments (CPE's) and base stations (BS's), can be used to jointly estimate the locations of the incumbent systems. Generally, there are four MAC management messages used for sensing, namely,                1. Bulk measurement request (BLM-REQ);        2. Bulk measurement response (BLM-RSP);        3. Bulk measurement report (BLM-REP); and        4. Bulk measurement acknowledgement (BLM-ACK).        
Using these four management messages, the sensing mechanism can be described as follows. When the BS requests one or more CPE's to sense a set of contiguous channel intervals, the BS transmits to those CPE's the BLM-REQ message, containing instructions on the type of measurements to be performed, as well as when and how long to perform. If the BS requires the CPE to acknowledge the receipt of the BLM-REQ message, this is done through the BLM-RSP message. The BLM-REP message then allows those CPE's to report back to the BS all measurement data they have collected as per the request in the BLM-REQ message. Finally, the BLM-ACK message is sent by the BS to those CPE's to confirm the receipt of the BLM-REP message.
Even though the conventional channel sensing method may be adequate in certain applications, there are various limitations, as discussed below. Therefore, an improved technique for channel sensing is desired.